[RE-wrenches] evergreen panels diode problems

[boB]

Darryl Thayer wrote:
> Hi all
> this all seems strange, perhaps the high positive voltage on the front of the cells causes a build up of charge attracting the negatively charged dust in the air.  Locally we have a DC power line each line either 450,000 volts either positive or Negative.  They reverse the polarity about once a month and when they do dust falls from one of the lines and the leakage current reduces.  The ground curren for this line is in the order of 100 amps? at the end of the month before reversal.  This is what i have been told by an eledctrician who works on the line.  I think the line is about 3000 amps.  
> Darryl 
>
>   

I know what it is ! Every two months you have to rotate your array.
Kind of like rotating your tires on your car.
Put the top panel on the bottom and vice-versa. LOL :)

I have read this short Sunpower explanation before, about the surface
polarization effect that reduces their efficiency in negative grounded
systems but here's the link anyway...

http://www.sunpowercorp.com/Smarter-Solar/The-SunPower-Advantage/~/media/Downloads/smarter_solar/polarization.ashx

I still don't know if there is a way around it, but I have a feeling 
there is not. They talk about running them at 1000V
negative for 1 hour to reverse the surface charge polarization. What 
happens when the modules are just being shipped
or sitting around un-connected for a long time ? That's probably OK, I 
would think. I would hope that one would not
have to de-polarize these once in a while as a matter of course.

boB

In part...

The high efficiency of SunPower’s A-300 solar cell is obtained in part 
by covering its front
surface with a proprietary coating which prevents the loss of the charge 
carriers generated by
sunlight. This layer performs much like a transistor that is turned off, 
preventing current flow. If
a large enough voltage is applied to the front of the cell, the 
“transistor” effectively turns on,
allowing charge carriers to recombine at the front surface. When this 
happens, surface
polarization reduces the output current of the cell. Also, like a 
transistor this effect can be fully
reversed and current returned to the original level.

AND

The polarization effect can be easily avoided by designing systems with 
proper grounding so that
modules only see negative voltage.